This invention relates to heat-treatment for foods. More particularly, the invention is directed to a continuous-processing type hot-water sterilizer and cooker for insuring sterilization and cooking of packaged foods in a manner such that the foods may retain the color, fragrance, taste, texture and quality similar to unprepared food.
Conventional sterilizers, having both a hot-water tank and a sterilization tank, require an installation of powerful hot-water pumps, large diameter pipes and large-size control valve because they must rapidly circulate hot water between these two tanks. It takes a considerable amount of time for sterilization tank to be filled to a given level with hot water.
This time increases when larger sterilizers are used to accomodate a greater volume of foods to be sterilized. Under this sterilization method, time needed to attain a given high temperature for sterilizing and the time needed to cool the sterilized foods to a given low temperature are considerable and consequently there is an impact on the quality of the foods. Namely, when hot water is placed in the sterilization tank, the foods on the bottom begin to cook immediately, those on the top later. Likewise, when the tank is emptied, the foods on the top lose temperature first, those on the bottom later. Therefore, there is a difference in cooking time between foods placed in the top and bottom of the product cage. Moreover the sterilization tank and its pipe arrangement are heated or cooled alternatively with hot water or cooling water, so that a large amount of heat energy is lost.